Progressive 2-pass decoder for real-time broadcast news captioning

This paper describes a 2-pass decoder that progressively outputs the latest available results used for real-time closed captioning of Japanese broadcast news. The decoder practically eliminates the disadvantage of multiple-pass decoders that delay a decision until the end of a sentence. During the first pass of search the proposed decoder periodically executes the second pass that rescores partial N-best word sequences up to that time. If the rescored best word sequence has words in common with the previous one, that part is regarded as likely to be correct and is decided to be a part of the final result. This method is not theoretically optimal but makes a quick response with a negligible increase in word errors. In a recognition experiment on Japanese broadcast news, the decoder worked with an average decision delay of 554 msec for each word and degraded word accuracy only by 0.22%